1. Field
Embodiments of the invention discussed herein relate to a scanner system and method for acquisition of inspection data using ultrasonic inspection or eddy current inspection methods.
2. Description of the Related Art
In destructive testing, defects are made apparent by stressing the object, for example, by bending or applying tension until any cracks present on the object break open. By comparison, nondestructive testing methods apply forces at such a low intensity that the object does not become damaged. Two such nondestructive testing methods that are relevant to the embodiments of the invention disclosed herein include ultrasonic inspection and eddy current inspection methods.
Ultrasonic inspection is carried out using an ultrasonic inspection probe and a scanner for tracking probe position, such that ultrasonic inspection data (e.g., waveforms representative of internal cracks or flaws, object thickness, etc.) generated by the ultrasonic inspection probe may be correlated with position data generated by the scanner and displayed to the operator and/or recorded for future use. Conventional ultrasonic inspection probes utilize a single transducer that transmits ultrasonic waves in a single, fixed direction. As a result, conventional ultrasonic inspection probes must be moved between each point in an inspection area and, consequently, are generally used with scanners capable of moving along two axes (i.e., x-axis and y-axis). Phased array ultrasonic inspection probes utilize multiple transducers which are pulsed individually by a controller such that the inspection probes can transmit a beam of ultrasonic waves into the object at various angles. As a result, phased array ultrasonic inspection probes can be used to inspect broad segments of an inspection area without being moved and are effective when used with scanners capable of movement along only one axis.
Like ultrasonic inspection, eddy current inspection is carried out using an inspection probe and a scanner for tracking probe position. Eddy current inspection probes utilize an excitation coil powered by alternating current to generate electric currents (eddy currents) in the object being inspected and a receiver coil to monitor variations in the resulting eddy currents. Eddy current inspection data (e.g., variations in the eddy currents representative of variations in composition or the presence of internal cracks or flaws) are then correlated with position data generated by the scanner and displayed to the operator and/or recorded for future use. Eddy current inspection probes, like conventional ultrasonic inspection probes, may be used with scanners capable of moving along two axes (i.e., x-axis and y-axis).
Existing scanners include a motor driven carriage fixed to a track that is mounted to the circumference of the object being inspected. The motor driven carriage is attached to the inspection probe and the inspection probe's position is tracked using the motor's controller or a rotary encoder that is mechanically coupled to gear teeth machined in the track. For conventional ultrasonic inspection and eddy current inspection, where scanners capable of movement along two axes are generally used, a second track, configured perpendicular to the first track, is fixed to the motor driven carriage.
Existing scanners are complex and have many interacting mechanical parts. As a result, they are costly to construct and require frequent repair and maintenance. The cost to develop and deploy these existing scanners has led to the deferment of ultrasonic inspection of thermal sleeves. Thermal sleeves are typically installed on pipes in locations where rapid changes in the temperature of water flowing in the pipes may cause fatigue cracks to grow. Occluded regions on the internal surfaces of thermal sleeves are susceptible to stress corrosion cracking. While it would be prudent to regularly inspect thermal sleeves to verify that stress corrosion cracking has not propagated, such inspection has been deferred until a lower cost scanner is available.
In addition, existing scanners require a minimum axial clearance of 7 inches to locate the track and motor. The large axial clearance required to locate existing scanners led to the deferment of inspection of certain welds in 14-inch, stainless steel piping that were required to be inspected as part of an in-service inspection program.
Two other existing scanners, which function differently than the above-mentioned scanners, include the Bettis “Free Motion Scanner” and Bettis “Orientation-Sensed Scanner.” The Free Motion Scanner is a hand-operated ultrasonic inspection device that may be moved over a complex object in an arbitrary pattern to generate an image of the object. The Free Motion Scanner is primarily intended for use in inspecting objects with complex surface contours, not objects such as pipes that have simple surface contours. See U.S. Pat. No. 6,122,967, which is hereby incorporated by reference. The Orientation Sensed Scanner is a single-axis scanner that senses the inclination of the probe as it is scanned, in contrast to existing scanners that sense the linear motion around the circumference of an object. However, current embodiments of the Orientation Sensed Scanner are not compatible with certain phased array ultrasonic inspection probes.
In light of the foregoing, there is a continuing need for cheaper, simpler scanners that can be used to carry out image inspection of an object, including ultrasonic inspection and eddy current inspection, within a small space envelope.